1. Field of the Invention
Aspects of the present invention relate to a method of and apparatus for recording/reproducing data on/from a holographic storage medium.
2. Description of the Related Art
In optical holography, data is stored within the volume of a recording medium instead of on the surface of the recording medium. Light carrying a signal interferes with reference light in the recording medium, thus generating an interference grating called a data page. A plurality of overlapping gratings can be recorded in the same volume by changing the optical characteristics of the reference light. Such a process is called multiplexing. In a data read operation, a single reference light is incident to the recording medium in the same condition as in a data write operation in order to generate diffracted light indicating a stored data page. The diffracted light is detected by a detection array that extracts stored data bits from a measured intensity pattern. The data page contains a number of data bits or pixels. The data storage capacity of the recording medium may increase by overlapping a plurality of data pages in the same volume of the recording medium. Holograms are recorded using a signal light including data and the reference light.
FIGS. 1A and 1B are reference diagrams explaining a recording operation and a reproducing operation in optical holography according to the prior art. In the recording operation illustrated in FIG. 1A, reference light R and signal light S interfere with each other and generate an interference pattern. The generated interference pattern is delivered to a recording medium. In the reproducing operation illustrated in FIG. 1B, reference light R irradiated to holograms recorded on the recording medium causes diffraction of the holograms, thereby generating output signal light S.
Recording on a holographic storage medium is performed by interference between the signal light and the reference light. The signal light is generated by a spatial light modulator in the form of a page composed of a plurality of pixels. The generated signal light interferes with the reference light on the holographic storage medium after passing through an optical system. An interference pattern generated in this way is recorded on the holographic storage medium. For reproduction, the reference light is incident to the recorded interference pattern and causes diffraction of the recorded signal light.
In hologram recording, the strength and phase of the signal light can be recorded in various ways, such as by changing the angle of reference light. Several hundreds to several thousands of holograms can be recorded in the same position in pages composed of binary data. The page can express information of a pixel with ‘on’ or ‘off’.
To record binary data on a holographic storage medium, a spatial light modulator generates binary data. A detector implemented with a Charge Coupled Device (CCD) or a Complementary Metal-Oxide-Semiconductor (CMOS) receives strength distribution with respect to light intensity in a binary data format, moves binary data to a corresponding position of the original page, and reads the binary data from the position.
If noise is generated when the spatial light modulator generates binary data or reproduces page data, data of the original page or the shape of the original page may be changed due to the noise, making the original data difficult to read. In particular, if additional information containing address information or modulation information of page data has an error due to noise, accuracy at which the detector reads the original data using the additional information may be degraded.